Plastic bearing

ABSTRACT

A reinforced plastic bearing comprising a generally cylindrical structure of plastic reinforced with glass fiber, provided with a tubular layer of polytetrafluoroethylene fibers embedded and secured in the plastic. In the fabrication of this bearing, the polytetrafluoroethylene fibers are intertwined and formed into a cord having an irregular outer surface. The intertwining binds the fibers into position to inhibit relative motion thereof such that the cord is characterized by multiple length portions of the fibers in the outer cord surface, having opposite end portions anchored in position. This cord is formed into a woven fabric which becomes said tubular layer and which is impregnated with the aforesaid plastic in liquid form, the plastic flowing into the irregularities and interstices in the fabric and cord so as intimately to enrobe substantial portions of the cords and fibers, thereby securing them in position relative to each other. One surface of the fabric tubular layer has exposed the lubricous fibers which provide the bearing surface. Retention of the polytetrafluoroethylene fibers against delamination is, in one preferred method, maximized by use of a mandrel having a highly polished layer of polytetrafluoroethylene thereon. In removing the hardened bearing composite from the mandrel, the integrity of the plastic matrix which secures the polytetrafluoroethylene fibers in place is maintained.

[4 1 Feb. 4, 1975 United States Patent Shobert 1 PLASTIC BEARINGABSTRACT A reinforced plastic bearing comprising a generally cylindricalstructure of plastic reinforced with glass fiber, provided with atubular layer of polytetraflu- [22] Filed:

Appl' 306295 oroethylene fibers embedded and secured in the plas-Related U.S. Application Data Division of Ser. No. 1,833, Jan. 9, 1970tic. In the fabrication of this bearing, the polytetrafluabandoned,oroethylene fibers are intertwined and formed into a which is acontinuation-impart of Ser. No. 800,955, cord having an irregular outersurface. The intertwin- Feb. 20, 1969, abandoned. ing binds the fibersinto position to inhibit relative motion thereof such that the cord ischaracterized by multiple length portions of the fibers in the outercord 00 00 oo 3 m mm 00 1 0m i 300 70 3 [51] Int. CL... Fl6c 13/00, Fl6c13/02, Fl6c 33/00 [58] Field of Search............. 1611/47, 88, 89, 92,93, 161/94, 95, 143, 189, 90, 96; 308/173, 238, DIG. 8; 156/148, 230,244, 247, 194

56 R f d One surface of the fabric tubular layer has exposed 1 e erencesthe lubricous fibers which provide the bearing surface.

UNITED STATES PATENTS Retention of the polytetrafluoroethylene fibersagainst delamination is, in one preferred method, maximized by use of amandrel having a highly polished layer of polytetrafluoroethylenethereon.

Runton............ Stanhope etal. In removmg the shobertmmw hardenedbearmg composite from the mandrel, the 970 T i integrity of the plasticmatrix which secures the polytetrafluoroethylene fibers in place ismaintained. Primary ExaminerGeorge F. Lesmes Assistant Examinerl. Cannon11 Clams 8 Drawmg Flgul'es PATENTED FEB 4l975 IN VEN TOR SAMUEL M BYWWPLASTIC BEARING This is a divisional application of application ser. no.l,833 filed .Ian. 9, 1970, now abandoned, which was acontinuation-in-part of application ser. no. 800,955, filed Feb. 20,1969, now abandoned, and is co-pending with divisional application ser.no. 287,566 filed Sept. 8, 1972.

BACKGROUND OF THE INVENTION 1. Field of the Invention The presentinvention relates to improvements in plastic bearings and moreparticularly to bearings which utilize fibers of a fluorocarbon resinsuch as polytetrafluoroethylene as the lubricous material.

2. DESCRIPTION OF THE PRIOR ART Reinforced plastic bearings are known.See, for instance, Shobert U.S. Pat. No. 3,131,979, issued May 5, I964,which discloses a hollow cylindrical bearing conventionally used tosupport the shafts of small electric motors and the like. This patentedbearing utilizes polytetrafluoroethylene-cotton threads to provide thelubricous bearing surface. These threads are bound or locked in positionby means ofa hardened plastic backing, the material of which intimatelysurrounds substantial portions of the fibers constituting the threadsand in particular penetrates and impregnates the cotton fibers. As aconsequence, the lubricous fibers are physically locked in position tothereby serve as the bearing material. As is well known, one of theproblems involved in the utilization of polytetrafluoroethylene fibersis that there is no known substance which will wet and chemically bondthereto. In the aforesaid Shobert patent, there is provided a means forlocking the lubricous fibers in place even though the plastic materialof the hard backing does not bond thereto.

SUMMARY OF THE INVENTION The present invention relates to an article ofmanufacture, such as a bearing or seal, which includes a lowfrictionstructure and a hard backing therefor of plastic material. Thelow-friction structure includes a layer of adjacent cords of fibers oflow coefficient of friction material, one surface of the layer being thebearing surface. Each of the cords is characterized by an irregularouter surface containing a plurality of raised and depressed portions.The fibers in each cord are anchored in place in relation to each otherby being bundled together and intertwined. The plastic material ofthehard backing is not bondable to the low-friction fibers. The cords andfibers constituting the layer are substantially embedded in and therebysecured by the plastic material. Portions ofthe fibers are exposedthrough the plastic material for defining the bearing surface.

Even though the material of the fibers, which preferably ispolytetrafluoroethylene, is not bondable chemically to any knownplastic, the fibers constituting the cord nevertheless are locked intoplace in the finished structure. This locking results from theparticular structure of the cord wherein the fibers are bundled togetherand intertwined such that they are substantially anchored againstrelative movement. Further, the resultant cord has an irregular outersurface such that by flowing liquid plastic therearound to provide asolidified mass, the cords in the first instance are anchored againstmovement by effectively being grasped by the hardened plastic and thefibers likewise are anchored by the plastic as well as by reason ofbeing anchored in the cords themselves.

Thus, it is possible, and indeed a unique feature of this invention, toutilize pure polytetrafluoroethylene fibrous material, without anydiluent therein such as cotton or other-synthetic fibers, for thepurpose of fabricating a bearing. This is in distinct contrast withprior art structures wherein bondable diluents such as cotton have beenused in order to anchor the polytetrafluoroethylene fibers in positionin a bearing surface.

It is an object of the present invention, therefore. to provide abearing utilizing fibers of fluorocarbon resin securely retained inposition in a manner that the quantity of these fibers that can beincorporated into a bearing surface is maximized thereby to provide ahigh degree of lubricity.

Another object of this invention is to provide a structure for securingfirmly and reliably maximum numbers of polytetrafluoroethylene fibers inposition in a bearing surface.

It is yet another object of this invention to provide a structurewhereby pure polytetrafluoroethylene strands without a bondable diluentsuch as cotton are used in the fabrication of bearings.

It is an object to provide a plastic composite bearing which includestwo different plastic or resinous materials not chemically or adhesivelybondable to each other, one of such materials being in the form ofstrands of low coefficient of friction material.

The above-mentioned and other features and objects of this invention andthe manner of attaining them will become more apparent and the inventionitself will be best understood by reference to the following descriptionof an embodiment of the invention taken in conjunction with theaccompanying drawings, wherein:

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a perspective illustrationof one bearing embodiment of this invention;

FIG. 2 is an end view thereof;

FIG. 3 is a side view;

FIG. 4 is a diagrammatical illustration, partly in vertical section, ofan apparatus used in the fabrication of this bearing;

FIG. 5 is a top plan view in diagrammatic form of the apparatus of FIG.4;

FIG. 6 is an enlarged view ofa small area of the interleaved threads orstrands in the bearing as woven by the apparatus of FIGS. 4 and 5;

FIG. 7 is a view of a short length of woven cord used in one embodimentof this invention;

FIG. 8 is a cross-section taken substantially along section line 88 ofFIG. 7;

The present invention is not limited to bearings but has application tomany different structures wherein bearing surfaces are required toreduce friction between moving surfaces. Also, while the bearingsdisclosed herein are primarily cylindrical in shape, the principles ofthis invention may be employed in making other shapes. Generallyspeaking, the bearing of this invention is fabricated of essentially thesame materials as are conventionally used in glass-reinforced plasticfishing rods, golf shafts, archery bows and arrows and the like. As anexception to this, however, a lamination of polytetrafluoroethylenestrands is uniquely arranged in the bearing and is combined with theglassreinforced plastic as will be described in more detail hereinafter.This invention constitutes an improvement on the method and structuresappearing in Shobert US. Pat. No. 3,131,979.

As shown in FIGS. 1, 2 and 3, the cylindrical bearing indicatedgenerally by reference numeral is composed of essentially twocontiguous, coaxial, tubular laminations 12 and 14. In one embodiment ofthis invention, which will later be described with particularity inconnection with FIGS. 7 and 8, the tubular lamination 14 is constructedprimarily of polytetraflu-- oroethylene cords in the form of a helicalbraid, the basic constituent being a strand of unbleached yarn which ina working embodiment of this invention has 60 filaments and a denier of400, there being no or zero twist in each strand. Such a strand ispresently being marketed under the trademark TEFLON by E. I. DupontDeNemours & Company, Inc. and is particularly described in a BulletinNo. T-lO dated April 1965 published by the same company and entitledProperties and Processing of Teflon Fiber. A plurality of these strands,in a working embodiment of this invention, is braided into a woven cord15 (FIGS. 7 and 8) having an outer surface which is irregular in thesense that it has a multiplicity'of longitudinally repeated raised anddepressed portions as well as some porosity provided by intersticesbetween fibers (filaments) and the strands themselves. This cordstructure will be explained in more detail later on.

The pattern of the braid forming lamination 14 is graphicallyillustrated in FIG. 6 and is shown as comprising a plurality of cords l5identified as 16 and 18, respectively, which are criss-crossed in wovenrelationship with each of the cords 16 and 18 alternately passing overand under each other as shown. Each cord 16, 18 follows the form ofahelix from one end ofthe bearing 10 to the other.

A second lamination 12 of helically braided glass threads coaxiallyoverlies lamination 14, these threads being braided together in the samepattern as shown in FIG. 6. Both of these laminations l2 and 14 areembedded in epoxy or polyester resin; however, the inner peripheralsurface 17 of the lamination 14 has exposed substantial portions of thepure polytetrafluoroethylene fibers which constitute the cords of thelamination 14.

The two laminations l2 and 14 are intimately and rigidly held togetherby means of the polyester or epoxy resin described hereinabove. Theglass threads preferably are of the glass yarn type, commonly referredto as roving, each thread being composed of a multiplicity of tinyelongated fibers, which, in effect, when bundled together form the finalcontinuous length of thread.

A method of fabricating the bearing of the materials thus far describedwill now be explained. Referring to FIGS. 4 and 5, a conventionalbraiding machine carries on its supporting table 20 a suitable number(six, in the present instance) of spools 22 and 28 ofpolytetrafluoroethylene cord 15 or glass thread depending upon theparticular stage of processing. At this stage, the spools have thepolytetrafluoroethylene cord 15 thereon. These particular spools 22 and28 are supported on suitable spindles 24 which fit into guide grooves 26which follow an undulating pattern as illustrated in FIG. 5. There aretwo series of spools on table 20, the spools 22 being characterizedherein as the outer spools while spools 28 are considered as the innerspools. By reference to FIG. 5, it is clearly shown that there are twodifferent undulating grooves 26 and 30 which cross over alternately asillustrated, and the spools 22 and 28, respectively, ride in thesegrooves.

A mandrel 32, cylindrically shaped, is passed through a clearanceopening 34 in table 20 as shown. An operator can hold this mandrel 32 inposition and operate it in the proper manner, as will be explained.

Woven cords 15 of polytetrafluoroethylene from the respective spools 22and 28 are individually affixed to the upper end of mandrel 32 by somesuitable means such as by tieing with a string or the like. This placesthe apparatus in readiness for operation.

In operation, mandrel 32 is slowly raised in the direction of the arrowF, while spools 22 and 28 are moved at a uniform rate of speed throughthe guiding grooves 26 and 30, respectively. Considering for a momentthe motion of one spool 22, it will form an interweaving braid with thecords from the spool 28. The mandrel 32 is continuously raised at auniform rate until the braid ing operation is completed for the entirelength thereof. The individual cords 15 are then cut and secured againstloosening by adhesive tape or string tied tightly around the mandrel,thereby leaving the mandrel 32 with a braided layer ofpolytetrafluoroethylene. In one embodiment, the cords extending in onehelical direction are parallel and contiguous as are the cords extendingin the opposite helical direction. This provides a woven fabric having aminimum of visible openings or pores therethrough; however, such poreswill in fact exist due to interstices between fibers, strands and in thewoven pattern itself. The denseness with which this weaving is performedmay be controlled to suit design requirements such as, for example, bycontrolling the speed at which the mandrel 32 is raised andthe tensionon the cords l6 and 18 as they pay off the spools 22 and 28.

As the next operation, the mandrel 32 with the first layer 14 of braidjust described is passed through another braiding apparatus identical tothe one disclosed in FIGS. 4 and 5 but which differs only in the respectthat the spools 22 and 28 contain glass threads.

By this means, a helical braid of glass thread is applied to the tubularcovering of polytetrafluoroethylene cords 15. Preferably, still a secondand in some instances a third layer of glass thread is applied to themandrel, thereby building up a substantial thickness of glass threadlamination in comparison with the polytetrafluoroethylene lamination.The radial thickness of the lamination 12 is therefore greater than thatof lamination 14. The mandrel with its composite covering is nextsubmerged into a catalyzed bath of liquid polyester or epoxy resinmaterial until the threads and cords are soaked or impregnated andembedded. Thereafter, the mandrel with its impregnated covering isplaced in a heated curing mold or oven until the resin is completelycured and hardened.

As the last step, the mandrel 32 is removed from the resin-supportedlaminations l2, 14, the resultant product being a hollow self-supportingtube composed of tubular laminations of resin, glass andpolytetrafluoroethylene materials.

Different techniques for impregnating or embedding the compositecovering on the mandrel 32 may be employed, such as vacuum impregnation,dipping, brushing and the like. It is important that the impregnation bethorough and that no voids or air pockets exist within the structure. Aswill later appear, it is important that the resin intimately andsubstantially engage the polytetrafluoroethylene for the purpose ofsecuring the same in position. It is important to note that thepolytetrafluoroethylene braid which is applied to the mandrel 32 isunder tension as it is intimately wound or wrapped onto the mandrel suchthat when the mandrel and its various braided laminations or layers areimpregnated with or embedded in the resin, the resin will not penetrateto the mandrel in the areas contacted by the polytetrafluoroethylenefibers but will leave the fibers which are in contact with the mandrelfree and clear of any resin. Thus, the finished surface will berelatively smooth and include the fibers and the cords as well as theresin in the spaces between the fibers and cords. The resin engagesintimately a sufficient portion of the polytetrafluoroethylene cords andfibers so as to secure these firmly in place, the resin in effectconstituting a matrix which holds the cords and fibers in position. Thehardened composite tube removed from the mandrel 32, if too long, can becut into shorter lengths so as to obtain the size bearings depicted inFIGS. 1 through 3.

The structure of the cord of FIGS. 7 and 8 will now be described.Strands of polytetrafluoroethylene yarn of, for example, 400 denier, 6Ofilaments or fibers with zero twist are braided together relativelytightly as shown in FIG. 7, these individual strands being indicated bynumeral 36. In a particular embodiment shown, six strands 36 are used.These strands are braided together using the apparatus of FIGS. 4 and 5.The finished cord is woven and has, therefore, a multiplicity of raisedand depressed portions in the outer surface which causes it to be quiteirregular. Inasmuch as there is zero twist in the individual strands 36,there are minute interstices between the fibers. There are alsointerstices between the strands 36 thereby producing in the cord 15 adegree of porosity and further surface irregularity.

As shown in FIG. 7, the individual strands 36 are undulated repeatedlythroughout the length of the woven cord 15, with portions thereof beingexposed at the cord surface and other portions being passed over andunder other strands so as to be physically intertwined therewith. Thisintertwining physically locks or anchors the strands and fibers inposition subject only to the slight displacement between fibers that ispermitted due to the fiber, strand and cord flexibility.

The fibers composing the strands 36 are bundled together such that eachstrand 36 is easily identified and can be individually handled. Thesestrands 36 are packaged on the spools 22 and 28 of FIGS. 4 and 5 fromwhich they are payed off in braiding or weaving the cord. Obviously, themandrel 32 would not be used in producing this braided cord 15.

The strands 36, and the fibers composing the strands 36, are anchored inthe braid weave of the cord 15 thereby resisting relative displacementtherebetween. As these cords 15 are woven into the braid liner orlamination 14 as previously explained, the fibers and strands 36 arefurther mechanically anchored relative to each other thereby furtherresisting relative displacement. By reason of the irregular outersurface of the cords 15 as well as the irregularities in the surfaces ofthe woven fabric, liquid resin which flows around these cords and intothe fabric penetrating to a certain degree the various intersticesbetween fibers, strands and cords, the individual fibers have severaldifferent forces or media tending to anchor them against displacement.

The irregularity in the cord surface permits resin to flow and formthereabout and thereinto thereby resisting either longitudinal ortransverse displacement of the cords 15. The same resin penetrates theinterstices between strands 36 holding them in position relative to eachother. Further, such resin penetrates at least some of the intersticesbetween fibers additionally anchoring them into place. The resin becomesa holding matrix which ultimately secures and anchors the fibers inposition in the bearing surface 16. Some strands and fibers will becompletely encased in the matrix. Thus, even though the resin of thehard backing I2 does not wet the fibrous material, still the material issecurely anchored in place without any other media such as cotton or thelike being required. This permits a maximum amount of lubricous fiberbeing disposed and distributed throughout the bearing surface H6 therebyenhancing the lubricous qualities of the bearing.

Another design is the strand 36 of pure polytetrafluoroethylene yarn,400 denier, 60 fibers twisted ll turns to the inch. This twisted strandor thread may be directly woven into the fabric of FIG. 6 applieddirectly to the mandrel 32. In a practical embodiment, the mandrel 32 ispassed through the braiding mechanism (FIGS. 4 and 5) three times toapply three layers of the polytetrafluoroethylene fabric, the twistedthreads in each instance being tensioned during weaving such that thethree layers will be intimately and securely compacted together and ontothe mandrel 32. The fibers in the woven cord are physically anchored inplace by reason of the intertwining and furthermore undulate irregularlyand randomly throughout the mass of the cords such that the resin whichforms the matrix anchors securely the fibers in place.

It is quite obvious that the cord of FIG. 7 made of six strands 36,whether they be twisted or untwisted, is much larger in cross-sectionalarea than is one of the twisted strands 36 alone.

A bearing made from a single layer of braided cord of FIG. 7 hasdifferent performance characteristics than one made ofthree layers oftwisted strands 36. Experiments have shown that the former bearing canwithstand higher radial loading when used as the shaft bearing in anelectric motor. The twisted strands 36 in plural layers tend to shear atthe interfaces under high loads. In contrast, the bearing having thebraided cord has greater wearlife, is more durable, and possessesgreater circumferential shear strength. One reason for these differencesis believed to be due to the fact that the braided cord of FIG. 7 madeof six interlocked strands 36, twisted or untwisted, is much larger incross-sectional area than is a single cord of twisted strand 36 wherebythe resin matrix with the fabric of the braided cord forms a moresecure, integrated composite that efficaciously resists delamination,shearing, etc.

The uniqueness of this invention is demonstrated by the fact that whenstrands 36 with zero twist are directly woven into a fabric such asbraided layer 14 without first having been incorporated into a structurelike cord 15, the fibers constituting the strands 36 disassociate fromthe hard backing 12 and in the interior of the bearing 10 appears as aloose, fuzzy or hairy mass. Such an arrangement is indeed unsatisfactoryin a bearing structure. In the present invention, the fibers and strands36 remain intact and provide a smooth and dimensionally stable surface.The reason the fibers and strands 36 become disassociated from theplastic backing 12 as just mentioned is that the plastic of backing 12during processing does not wet or chemically bond to thepolytetrafluoroethylene strands. In the past, in order to secure thestrands in place, threads and fabrics made of this material havecontained cotton or some similar bondable material which whenimpregnated with the plastic served to lock the polytetrafluoroethylenefibers in place. Attempts to secure the polytetrafluoroethylene fibersin place without using such bondable material have been unsuccessfulespecially in connection with high speed bearings.

The present invention makes it possible to obtain a maximum quantity ofpolytetrafluoroethylene fiber in the lubricous surface of the bearing.This increases the bearing lubricity, the wear life of the bearing andthe speeds at which the bearings can be used. Dimensional stability isenhanced by maintaining the thickness of the braid layer 14 to a minimumwhich means the cord 15 size and the number of strands 36 should also bekept to a minimum.

In another embodiment, the bearing surface includes tiny islands ofpolytetrafluoroethylene in the form of powder or particles. Theseparticles in combination with the polytetrafluoroethylene fibers providea highly lubricous bearing surface. The method of incorporating theseparticles is disclosed and claimed in Tunis application Ser. No.706,422, filed Feb. 19, 1968, now US. Pat. No. 3,533,668, entitledReinforced Plastic Bearing and Method for Fabricating Same. Theseparticles are incorporated into the structure of this invention asfollows. Prior to applying the braided layer 14 to the mandrel, thelatter is immersed in a bath of liquid resin material containing finelydivided and evenly dispersed polytetrafluoroethylene particles. Themandrel is removed from the bath and placed in the braiding machine ofFIGS. 4 and 5 and the cords 16 and 18 are braided onto the mandrel. Theliquid resin suspension which coats the mandrel is squeezed outwardlythrough and between the cords l6 and 18 which form the layer 14 therebyserving to at least partially impregnate the layer 14. In oneworkingsystem, the liquid resin is catalyzed epoxy for producing athixotropic material having a high viscosity. The preferred viscosityofthe resin material is approximately 500 to 1,000 cps. Thepolytetrafluoroethylene particles are of a size of about 1 micron orless in diameter.

Immediately following the braiding of the layer 14, the assemblyincluding mandrel 32 is again immersed in a bath of liquid resincontaining polytetrafluoroethylene particles, as just described, andthen agitated sufficiently to insure full impregnation of the layer 14and the cords l6 and 18 thereof.

The mandrel composite now thoroughly impregnated and embedded throughoutin the liquid suspension is removed from the bath and once again placedin the braiding machine for the application of the layer or layers 12.When the application of the layers of glass braid has been completed,the entire mandrel and layer assembly is once again immersed in a bathofliquid resin which, in this instance, does not contain thepolytetrafluoroethylene particles. However, this resin preferably is ofthe same composition as that which was used in the suspension for layer14. The mandrel composite is now treated by heating or otherwise to cureand solidify the resin.

In the initial application of the braided cords 15 16, 18) to the wettedmandrel, the wrapping force is sufficient to place these cords 16 and 18into intimate contact with the mandrel surface such that the wet resinis squeezed upwardly past the cords 16 and 18 at the points where theyengage the mandrel surface. These cords also may flatten and conformsomewhat to the surface of the mandrel 32. This assures, then, that theinner surface of the layer 14 has polytetrafluoroethylene materialsufficiently close to the inner surface of the bearing to provide thenecessary lubricity. The solidified resin thereby becomes a holdingmatrix not only for the polytetrafluoroethylene fibers but also theparticles. This provides additional lubricous material in the bearingsurface.

ln a working system, the liquid resin contained a percentage ofpolytetrafluoroethylene particles ranging from 20% to 50% By volume. Byway of upper and lower limits of polytetrafluoroethylene particlecontent, too much such material will result in destroying the physical,matrix or encapsulating characteristics of the resin, thereby leading todimensional instability of the entrained polytetrafluoroethylene.

lf too small an amount of polytetrafluoroethylene powder is used, thelubrication qualities are diminished.

In a further embodiment, a problem, not heretofore recognized, has beensolved for providing a further improvement in anchoring the purefluorocarbon fibers securely in place. This can best be explained byconsidering contrasting arrangements.

Conventional mandrels 32 are of highly polished steel which, in someinstances, are coated with a release wax commonly used in thefiber-reinforced polyester art. Such a conventional mandrel used astaught in the preceding will yield the results explained. Furtherimprovement in the results, however, are secured by using the samemandrel having secured on the exterior a smooth film or layer ofpolytetrafluoroethylene. Such polytetrafluoroethylene films and layersare conventionally used in the aforesaid art and also in cookware toprevent sticking of cooked or fried foods. Such polytetrafluoroethylenelayers may be made to different degrees of smoothness, it being desiredin the present instance that the material as applied to the mandrel 32have the smoothest possible surface. Known techniques can be used tocover the mandrel 32 with the material.

This mandrel 32 having the polytetrafluoroethylene layer thereon isutilized in the fabrication of the bearings, as already explained.However, it has been discovered that the bearing surface formed adjacentto the polytetrafluoroethylene layer on the mandrel has a glossysmoothness as contrasted with a duller finish as results from use of aconventional mandrel 32 having a polished steel surface of the samedegree of smoothness. Further contrast is found in the fact that thepolytetrafluoroethylene mandrel provides no trace of de' laminations asevidenced by fuzzing of the polytetrafluoroethylene fibers, whereas inthe use of the highly polished steel mandrels, close inspection of thebearing surface by the use of magnifying lenses reveals a certaindullness therein and some polytetrafluoroethylene fibers having moreexposure through the resin matrix than do the fibers in the surface madeon the polytetrafluoroethylene mandrel.

Experiments have proven that there is less tendency of thepolytetrafluoroethylene fibers to delaminate and fuzz in the bearingsmade on the mandrel coated with the polytetrafluoroethylene materialthan with the highly polished steel mandrel having the usual wax releaseagent. While the reason for this is not entirely understood, it isbelieved there is less tendency of the polyester and epoxy resin to wetthe polytetrafluoroethylene mandrel than is true of the steel mandrelconventionally treated with a release agent such that when thepolytetrafluoroethylene mandrel is withdrawn from the hardened bearingcomposite. there is less tendency to disturb the hardened resin surfacethereby maintaining the integrity of the matrix which secures thepolytetrafluoroethylene fibers in place. It is theorized that in the useof a highly polished steel mandrel conventionally treated, microscopicparticles of the resin surface are torn away as the mandrel is removedfrom the hardened bearing composite, such that many of thepolytetrafluoroethylene fibers have less matrix resin in contacttherewith than is true when the polytetrafluoroethylene coated mandrelis used. Even though the polish on the steel may be higher than that ofthe polytetrafluoroethylene coating, still the dullness of the bearingsurface suggests that minute particles or portions of the polyester orepoxy resin are separated from the bearing surface at the time themandrel is removed.

Recapitulating, use of the polytetrafluoroethylene coated mandrel 32provides a release which does not tear away minute particles of thematrixing resin when the mandrel is stripped out of the bearing piece.In the use of mandrels which do not have as good releasecharacteristics, stripping the mandrel out of the finished piece resultsin tearing away minute particles of the matrixing resin which in turncan result in dislodgement of the polytetrafluoroethylene fibers or atleast releases them such that delamination and fuzzing can occur. Thus,it is theorized that there is a definite connection between the securingof the pure polytetrafluoroethylene fibers in position and the releaseproperties of the mandrel 32. In use of the coated mandrel, the tinyislands or particles of matrixing resin which serve to encapsulate thetiny polytetrafluoroethylene fibers are not disturbed, thereby resultingin the retention of the matrix integrity.

Based on the theory that the degree of smoothness as well as the mandrelmaterial are characteristics important in maintaining the integrity ofthe resin matrix it indeed is intended that alternative equivalentmaterials be included within the comprehension of this invention. Inparticular, polytetrafluoroethylene resin has been identified as onespecific material that will produce the salutary results. Othermaterials having the potential of being equally efficacious is anotherfluorocarbon resin known as fiuoroethylene polymer.

Recapitulating, in providing an improved bearing utilizingpolytetrafluoroethylene as the lubricous material, certain designdesiderata are important as follows. The matrixing resin should beundisturbed as much as possible upon withdrawal of the mandrel from thebearing piece. The fibers of the polytetrafluoroethylene should beformed into a cord having radial depth with each fiber alternatingthroughout the cord mass from deep embedment to being exposed at thesurface thereof, this being accomplished by forming a woven cord asshown in FIG. 7. The cord composed of undulated, in-

tertwined, interlocked fibers, having radial depth, is intimatelyengaged by encapsulating matrix resin, thereby anchoring in place thosepolytetrafluoroethylene fibers exposed at the bearing surface.

This invention is generally unique in that it provides methods andstructures for joining two materials toether which are not chemically oradhesively bondable to each other, examples of these materials being theones identified hereinabove. This invention, therefore, is not limitedto the particular materials in the fibers, strands, cords and plasticbacking, as there are other materials of like descriptive property whichare not chemically bondable but which can be physically secured togetheras comprehended by this invention.

The word "intertwine" appearing in the claims and written description isused in its broadest sense to means to unite or become mutually involvedby twining one with another, to entangle, interlace, intertwist, or tointerweave.

The material polytetrafluoroethylene is a fluorocarbon resin having lowcoefficient of friction properties. It is intended that othercompositions of this resin exhibiting the properties ofpolytetrafluoroethylene be included in the coverage provided by thispatent as well as other plastic or resinous materials which possessproperties of low coefficient of friction.

The cord 15 design of FIGS. 7 and 8 of only polytetrafluoroethylenefibers as described provides for a maximum amount of lubricous materialin the bearing surface since no diluent such as cotton is used therein.The cord 15 is relatively large in cross-section thereby providing arelatively deep (radially) mass of bearing material providing acorresponding degree of wear life. The fibers constituting the bearingmass are held in place by reason of the intertwining provided by thecord configuration and the intimate embedment in the plastic backing.Delamination is thus avoided.

Even though no cotton or other bondable mmaterial is used in the cord15, the lubricous fibers are firmly secured in place in a bearing massof maximized radial depth as well as in lubricous material.

While there have been described above the principles of this inventionin connection with specific apparatus, it is to be clearly understoodthat this description is made only by way of example and not as alimitation to the scope of the invention.

What is claimed is:

1. An article of manufacture comprising a lowfriction structure and ahard backing therefor, said hard backing including a plastic material,said lowfriction structure having a bearing surface comprising adjacentcords of strands of low coefficient of friction material, each strandconsisting of low coefficient of friction material in fiber form andsaid low coefficient of friction material including fluorocarbon resin,each cord having an irregular outer surface containing a plurality ofraised and depressed portions, said strands in each cord being woventogether for locating said fibers in place in relation to each other,said cords being interlaced together in a woven fabric which furtheranchors said fibers against displacement, said cords and fibers beingsubstantially embedded in said plastic material such that the lattermechanically secures said cords and fibers in position, said fibersbeing undulated throughout the length of said cords with portions ofsaid fibers being exposed through said plastic material to define saidbearing surface and other portions being 11 fully embedded in saidplastic material, said plastic material not being chemically oradhesively bonded to said fibers or cords.

2. The article of claim 1 in which the strands of each cord are braidedtogether, at least a portion of said fibers and cords having intersticestherebetween which are substantially filled by said plastic material,said plastic material not being chemically or adhesively bonded to anyof said fibers or cords.

3. The article of claim 2 in which said hard backing is of annular shapeand having inner and outer peripheral surfaces, said low-frictionstructure also being annular and secured to one of said peripheralsurfaces, said cords being braided into a seamless cylinder, one portionof said cords extending in the form of a helix in one circumferentialdirection alternately over and under another portion of cords, saidcords being contiguous so as to provide a substantially continuous,

bearing surface of low-friction fibers.

twisted thereby further anchoring said fibers relative to each other.

5. The article of claim 1 in which each strand is of about 400 denier,and includes about 60 fibers.

6. The articles of claim 1 in which said hard backing is of annularshape and having inner and outer peripheral surfaces, said low-frictionstructure also being annular and secured to one of said peripheralsurfaces.

7. The article of claim 6 in which said low friction material ispolytetrafluoroethy'lene.

8. An article or manufacture comprising a lowfriction structure and ahard backing of fiber reinforced plastic therefor, said low-frictionstructure having a bearing surface comprising adjacent cords of strandsconsisting of polytetrafluoroethylene fibers, each cord having anirregular outer surface containing a plurality of raised and depressedportions, said strands in each cord being braided together for locatingsaid fibers in place in relation to each other, said cords beinginterlaced together in a woven fabric which further anchors said fibersagainst displacement, said cords and fibers being substantially embeddedin said plastic material such that the latter mechanically secures saidcords and fibers in position, said fibers being undulated throughout thelength of said cords with portions of said fibers being exposed throughsaid plastic material to define said bearing surface and other portionsbeing fully embedded in said plastic material, said plastic material notbeing chemically or adhesively bonded to said fibers or cords.

9. The article of claim 8 in which said hard backing is of annular shapeand having inner and outer peripheral surfaces, saidlow-frictionstructure also being annular and secured to one of said peripheralsurfaces, said cords being braided into a seamless cylinder, one portionof said cords extending in the form of a helix in one circumferentialdirection alternately over and under another portion of said cords, saidcords being contiguous so as to provide a substantially continuousbearing surface of low-friction fibers.

10. The article of claim 8 in which said strands are twisted therebyfurther anchoring said fibers relative to each other.

11. The article of claim 8 in which said hard backing is of annularshape and having inner and outer peripheral surfaces, said low-frictionstructure also being annular and secured to one of said peripheralsurfaces.

1. AN ARTICLE OF MANUFACTURE COMPRISING A LOW-FRICTION STRUCTURE AND AHARD BACKING THEREFOR, SAID HARD BACKING INCLUDING A PLASTIC MATERIAL,SAID LOW-FRICTION STRUCTURE HAVING A BEARING SURFACE COMPRISING ADJACENTCORDS OF STRANDS OF LOW COEFFICIENT OF FRICTION MATERIAL, EACH STRANDCONSISTING OF LOW COEFFICIENT OF FRICTION MATERIAL IN FIBER FORM ANDSAID LOW COEFFICIENT OF FRICTION MATERIAL INCLUDING FLUOROCARBON RESIN,EACH CORD HAVING AN IRREGULAR OUTER SURFACE CONTAINING A PLURALITY OFRAISED AND DEPRESSED PORTIONS, SAID STRANDS IN EACH CORD BEING WOVENTOGETHER FOR LOCATING SAID FIBERS IN PLACE IN RELATION TO EACH OTHER,SAID CORDS BEING INTERLACED TOGETHER IN A WOVEN FABRIC WHICH FURTHERANCHORS SAID FIBERS AGAINST DISPLACEMENT, SAID CORDS AND FIBERS BEINGSUBSTANTIALLY EMBEDDED IN SAID PLASTIC MATERIAL SUCH THAT THE LATTERMECHANICALLY SECURES SAID CORDS AND FIBERS IN POSITION, SAID FIBERSBEING UNDULATED THROUGHOUT THE LENGTH OF SAID CORDS WITH PORTIONS OFSAID FIBERS BEING EXPOSED THROUGH SAID PLASTIC MATERIAL TO DEFINE SAIDBEARING SURFACE AND OTHER PORTIONS BEING FULLY EMBEDDED IN SAID PLASTICMATERIAL, SAID PLASTIC MATERIAL NOT BEING CHEMICALLY OR ADHESIVELYBONDED TO SAID FIBERS OR CORDS.
 2. The article of claim 1 in which thestrands of each cord are braided together, at least a portion of saidfibers and cords having interstices therebetween which are substantiallyfilled by said plastic material, said plastic material not beingchemically or adhesively bonded to any of said fibers or cords.
 3. Thearticle of claim 2 in which said hard backing is of annular shape andhaving inner and outer peripheral surfaces, said low-friction structurealso being annular and secured to one of said peripheral surfaces, saidcords being braided into a seamless cylinder, one portion of said cordsextending in the form of a helix in one circumferential directionalternately over and under another portion of cords, said cords beingcontiguous so as to provide a substantially continuous bearing surfaceof low-friction fibers.
 4. The article of claim 2 in which said strandsare twisted thereby further anchoring said fibers relative to eachother.
 5. The article of claim 1 in which each strand is of about 400denier, and includes about 60 fibers.
 6. The articles of claim 1 inwhich said hard backing is of annular shape and having inner and outerperipheral surfaces, said low-friction structure also being annular andsecured to one of said peripheral surfaces.
 7. The article of claim 6 inwhich said low friction material is polytetrafluoroethylene.
 8. ANARTICLE OR MANUFACTURE COMPRISING A LOW-FRICTION STRUCTURE AND A HARDBACKING OF FIBER REINFORCED PLASTIC THEREFOR, SAID LOW-FRICTIONSTRUCTURE HAVING A BEARING SURFACE COMPRISING ADJACENT CORDS OF STRANDSCONSISTING OF POLYTETRAFLUOROETHYLENE FIBERS, EACH CORD HAVING ANIRRECULAR OUTER SURFACE CONTAINING A PLURALITY OF RAISED AND DEPRESSEDPORTIONS, SAID STRANDS IN EACH CORD BEING BRAIDED TOGETHER FOR LOCATINGSAID FIBERS IN PLACE IN RELATION TO EACH OTHER, SAID CORDS BEINGINTERLACED TOGETHER IN A WOVEN FABRIC WHICH FURTHER ANCHORS SAID FIBERSAGAINST DISPLACEMENT, SAID CORDS AND FIBERS BEING SUBSTANTIALLY EMBEDDEDIN SAID PLASTIC MATERIAL SUCH THAT THE LATTER MECHANICALLY SECURES SAIDCORDS AND FIBERS IN POSITION, SAID FIBERS BEING UNDULATED THROUGHOUT THELENGTH OF SAID CORDS WITH PORTIONS OF SAID FIBERS BEING EXPOSED THROUGHSAID PLASTIC MATERIAL TO DEFINE SAID BEARING SURFACE AND OTHER PORTIONSBEING FULLY EMBEDDED IN SAID PLASTIC MATERIAL, SAID PLASTIC MATERIAL NOTBEING CHEMICALLY OR ADHESIVELY BONDED TO SAID FIBERS OR CORDS.
 9. Thearticle of claim 8 in which said hard backing is of annular shape andhaving inner and outer peripheral surfaces, said low-friction structurealso being annular and secured to one of said peripheral surfaces, saidcords being braided into a seamless cylinder, one portion of said cordsextending in the form of a helix in one circumferential directionalternately over and under another portion of said cords, said cordsbeing Contiguous so as to provide a substantially continuous bearingsurface of low-friction fibers.
 10. The article of claim 8 in which saidstrands are twisted thereby further anchoring said fibers relative toeach other.
 11. The article of claim 8 in which said hard backing is ofannular shape and having inner and outer peripheral surfaces, saidlow-friction structure also being annular and secured to one of saidperipheral surfaces.